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Take Heed City Dwellers: It’s Hot and Getting Hotter

Terri Hansen

8/22/14

Buildings, roads, and other infrastructure that make up urban environments typically make cities hotter than surrounding rural areas, a condition known as an urban heat island.

If you live in Albuquerque, Denver, Minneapolis, Portland or Seattle, you inhabit a notably hotter environment than do your rural neighbors during the hottest months of the year, thanks to the urban heat island effect. Other cities with large Native American populations like Tulsa, Oklahoma City, and Tucson suffer, too.

It’s not just increased heat, either, to worry about. These hotter urban temperatures, expected to become more intense, frequent and long-lasting, raise the risk for dangerous ozone air pollution, according to a new report, Summer in the City, from Climate Central, a research and journalism organization.

The report found rising greenhouse gas emissions are projected to drive average U.S summer temperatures even higher in the coming decades, exacerbating urban heat islands and their associated health risks. Heat is the number one weather-related killer in the U.S., and the hottest days, particularly days over 90°F, are associated with high levels of air pollution that can trigger asthma attacks, heart attacks and other serious health impacts.

Albuquerque, a city that according to the 2010 Census is six percent American Indian, gets as much as 22° Fahrenheit hotter than neighboring rural areas, and averages 5.9° hotter. The city, which is ranked number two in having the biggest difference between urban and rural temperatures, experiences higher nighttime temperatures as well.

On average across all 60 cities, urban summer temperatures were 2.4°F hotter than rural temperatures.

Cities tend to have fewer trees and less vegetation that provide shade and cooling, and more industrial heat sources, including cars and air conditioners. In sunlight, concrete, asphalt, and shingled roofs can get much hotter than vegetated areas, causing surface temperatures in cities to be several degrees hotter in the midday than in rural areas. After sunset, these same materials release heat more slowly, keeping urban air temperatures higher overnight than in most rural areas.

“Climate change is warming the entire planet, rural and urban areas alike,” said Alyson Kenward, lead author of the report, in a statement. “But thanks to the dual action of urbanization and climate change, cities are not just hotter, they are getting hotter faster: 45 of 60 cities we analyzed were warming at a faster rate than the surrounding rural land.”

It’s an environmental justice issue, according to a report published in the journal Environmental Health Perspectives in July 2013. The study, which omitted Native Americans, found that blacks, Asians and Latinos were more likely to live in urban heat islands. The same neighborhoods shared by many urban Natives.

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